1. Field of the Invention
The present invention relates to new binder compositions of polyacrylate polyols and crosslinking agents, a process for their preparation and their use for the production of coatings.
2. Description of the Prior Art
The advantage of high-solids polyacrylate resins is to be seen in the reduction in the emission of organic compounds, preferably solvents, during the application of the coating. To obtain these high-solids coating formulations, corresponding polyacrylate resins with low viscosities, i.e. low molecular weights, should be used.
It is known that free-radical solvent polymerization can be used for the preparation of low-viscosity polymers (e.g. EP-A 408 858, EP-A 398 387 and U.S. Pat. No. 4,145,513). The properties of these polymers are impaired by the use of considerable amounts of polymerization regulators and secondary products thereof. In particular, the thiols employed as polymerization regulators may smell nauseous or may even be toxic. In EP-A 225 808, EP-A 225 809 and EP-A 778 298, xcex1-olefins, such as e.g. 1-octene or 1-decene, which have no unpleasant smell, are therefore used as regulators. However, two-component polyurethane (2C PU) lacquers based on the polyacrylate resins according to EP-A 225 809 and aliphatic polyisocyanates have too slow a physical drying to be employed e.g. for use in car repair and large vehicle lacquering. The drying of 2C PU lacquers according to EP-A 778 298 also no longer completely meets current application requirements in this respect and is therefore in need of improvement.
EP-A 635 523 and EP-A 638 591 describe high-solids polyacrylate resins which are prepared by bulk polymerization and are then diluted with a suitable solvent.
EP-A 635 523 describes the effect, known from solvent polymerization, of the preparation of high-solids polyacrylate resins with a unimodal narrow distribution using peroxides containing tert-amyl groups, but applied to bulk polymerization. As expected, it was demonstrated that lower-viscosity polyacrylate resins are obtained with peroxides containing tert-amyl groups than with peroxides containing tert-butyl groups. However, bulk polymerization has disadvantages compared with solvent polymerization, in particular with respect to the removal of the heat of reaction. The polyacrylate resins prepared in the examples of the above mentioned application have viscosities at 23xc2x0 C. of between 2,790 and 9,130 mPa.s at a solids content of 70 wt. %, and are therefore in the medium-solids than in the high-solids range. They do not meet the current requirements of high-solids lacquers.
EP-A 171 847 and EP-A 638 591 describe high-solids copolymers which have a relatively low viscosity at a high solids content due to the use of (meth)acrylate monomers with sterically bulky (cyclo)alkyl radicals. However, the resistance of such copolymers to solvents and chemicals no longer completely meets the current requirements of highly resistant car repair lacquers. In the preparation of the copolymers according to EP-A 638 591 by bulk polymerization, a monoepoxide (Cardura E 10) is initially introduced into the reaction vessel as the reaction medium in all the examples described. During the polymerization this monoepoxide reacts with the (meth)acrylic acid metered in and is thus incorporated into the polyacrylate. Predominantly secondarily bonded hydroxyl groups are formed by this reaction, and, in addition to the primary hydroxyl groups or secondary hydroxyl groups introduced by hydroxy-functional monomers (hydroxyethyl methacrylate and hydroxypropyl methacrylate respectively), are available for the reaction with the polyisocyanate used as a crosslinking agent.
However, secondary hydroxyl groups have a significantly lower reactivity towards polyisocyanates than primary hydroxyl groups. 2C PU lacquers which are cured at low temperatures (car repair and large vehicle lacquering, wood lacquering) and are based on polyacrylate resins with predominantly secondarily bonded hydroxyl groups therefore achieve an adequate crosslinking density and a satisfactory resistance to solvents only after several days. Precisely in car repair and large vehicle lacquering, however, a rapid chemical crosslinking is also urgently necessary, in addition to a rapid physical drying, in order thus to allow the vehicle to be further used as quickly as possible.
It is therefore the object of the invention to provide new binder compositions based on hydroxy-functional copolymers and (cyclo)aliphatic lacquer polyisocyanates which give high-solids lacquers which, in addition to a rapid physical drying, also show a rapid chemical crosslinking at room temperature (23xc2x0 C.) and an excellent resistance to solvents after a short curing time of 1 to 2 days.
New high-solids binder compositions, which can be cured to give high-quality coatings are obtained by combination of the OH-functional binder components essential to the invention with polyisocyanates. In addition to outstanding optical properties of the films and a high resistance to solvents and chemicals, these coatings show a very rapid physical drying and chemical crosslinking at room temperature and a good surface hardness.
The very good overall profile of properties of the resulting coating films, such as hardness, elasticity and resistance to chemicals, solvents and weathering, allows use in vehicle lacquering, preferably in car repair and large vehicle lacquering. Other fields of use lie in the sectors of general industrial lacquering, corrosion protection and wood and furniture lacquering, it also being possible for other crosslinking resins to be used as the polyisocyanates.
The invention relates to a binder composition containing
A) 50 to 90 parts by wt., preferably 90 to 60 parts by wt. of OH-functional graft copolymer resins prepared by copolymerization of
a) 0.1 to 10 parts by wt. of at least one optionally functional polybutadiene with a number-average molecular weight of 500 to 10,000 and a structure which is at least 20% 1,2-vinyl,
b) 5 to 60 parts by wt. of at least one unsaturated aromatic monomer,
c) 10 to 50 parts by wt. of at least one hydroxyalkyl ester of acrylic and/or methacrylic acid having 2 to 4 C atoms in the hydroxyalkyl radical and a primary hydroxyl group,
d) 5 to 70 parts by wt. of at least one cycloaliphatic ester of acrylic and/or methacrylic acid having 1 to 12 C atoms in the alcohol component,
e) 5 to 50 parts by wt. of at least one aliphatic ester of acrylic and/or methacrylic acid having 1 to 8 C atoms in the alcohol component,
f) 0.1 to 5 parts by wt. of at least one xcex1,xcex2-mono-olefinically unsaturated mono- or dicarboxylic acid having 3 to 7 C atoms and/or at least one maleic acid or fumaric acid half-ester having 1 to 14 C atoms in the alcohol radical and
g) 0 to 40 parts by wt. of further copolymerizable olefinically unsaturated compounds and
B) 10 to 50 parts by wt. of a polyfunctional crosslinking agent or crosslinking agent mixture,
the sum of the parts by wt. of components A) and B), based on the weight of A) and B), and the sum of the parts by wt. of components a) to g) in each case being 100.
The invention also relates to a process for the preparation of the binder compositions according to the invention characterized in that the graft copolymers A) described above are prepared by free-radical polymerization in organic solvents at temperatures between 150 and 240xc2x0 C. and are combined with suitable crosslinking resins B).
The invention also provides the use of the binder compositions according to the invention to produce lacquers for vehicle lacquering, in particular for car repair and large vehicle lacquering, for general industrial, wood and furniture lacquering and in the corrosion protection sector.
A large number of polyfunctional crosslinking agents are suitable according to the invention, including aminoplast resins, such as alkoxylate melamine resins, melamine-formaldehyde condensation products, urea resins, guanidine resins, phenoplast resins, resol resins and, preferably, optionally blocked polyisocyanate resins, preferably oligomeric isocyanates with a biuret, allophanate, uretdione, urethane and/or isocyanurate or iminooxadiazinedione structure.
The graft copolymers A) differ quite substantially in their chemical composition both from the polyacrylate polyols of EP-A 225 809 and EP-A 778 298 and from the bulk copolymers of EP-A 635 523 and EP-A 638 591. In respect of the lacquering properties, in particular the rate of drying and the resistance to solvents, advantages result over the products of the documents mentioned, as is demonstrated in corresponding comparison examples.
Similar but not identical binder compositions are described in EP 279 311. Furthermore, the binder compositions according to the invention are intended in particular for a field of use which is not referred to in the earlier document mentioned, because the lacquers described therein have too long a drying time and give highly flexible coating films with too low a hardness.
The graft copolymer resins A) essential to the invention can be prepared by copolymerization of constituents a) to g) by conventional processes. Free-radical polymerization in solution is preferred. In this process, monomeric and oligomeric units are copolymerized at temperatures of 140 to 240xc2x0 C. in the presence of reagents which form free radicals.
The polyacrylate resins A) include the following components:
Component a) includes one or more optionally functional polybutadienes with a number-average molecular weight of 500 to 5,000, preferably 500 to 3,000, more preferably 500 to 2,000. The polybutadienes have a structure which is at least 20% 1,2-vinyl, preferably at least 30% 1,2 vinyl and more preferably at least 40% 1,2-vinyl and most preferably 45%1,2-vinyl.
Component b) includes an unsaturated aromatic monomer, which is preferably styrene. It is used in amounts of 5 to 60 parts by wt., preferably 10 to 40, more preferably 15 to 35, and most preferably 15 to 25 parts by wt.
Component c) includes a hydroxyalkyl ester of acrylic and/or methacrylic acid having 2 to 4 C atoms in the hydroxyalkyl radical and a primary hydroxyl group is used. Preferably component c) is hydroxyethyl acrylate, hydroxyethyl methacrylate, butane-1,4-diol monoacrylate or mixtures thereof. More preferably it is hydroxyethyl acrylate, hydroxyethyl methacrylate, or mixtures thereof. It is used in amounts of 10 to 50, preferably 10 to 45, more preferably 20 to 40, most preferably 25 to 35 parts by wt.
Component d) includes a cycloaliphatic ester of acrylic and/or methacrylic acid having 1 to 12 C atoms in the alcohol component, preferably isobornyl acrylate, isobornyl methacrylate, cyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate or mixtures thereof, more preferably isobornyl acrylate. It is used in amounts of 5 to 70, preferably 10 to 50, more preferably 15 to 45, most preferably 20 to 30 parts by weight.
Component e) includes at least one aliphatic ester of acrylic and/or methacrylic acid having 1 to 8 C atoms preferably, 1 to 4 C atoms in the alcohol component. It is used in amounts of 5 to 50 parts by wt, preferably 10 to 40 parts by wt., and more preferably 15 to 25 parts by wt.
Component f) includes at least one xcex1,xcex2-mono-olefinically unsaturated mono- or dicarboxylic acid having 3 to 7 C atoms and/or at least one maleic acid or fumaric acid half-ester having 1 to 14 C atoms in the alcohol radical, preferably acrylic acid, methacrylic acid, or a maleic or fumaric acid half-ester having 1 to 8 C atoms in the alcohol component or mixtures thereof, and more preferably acrylic acid, methacrylic acid or mixtures thereof. It is used in amounts of 0.1 to 5 parts by wt., preferably 0.3 to 4 parts by wt., more preferably 0.5 to 3 parts by wt. and most preferably 0.5 to 2 parts by wt.
Component g) is an optional component and can include other copolymerizable olefinically unsaturated compounds, preferably acrylonitrile, methacrylonitrile, hydroxypropyl (meth)acrylate (only up to 10 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 10 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 8 C atoms in the alcohol radical or mixtures thereof. More preferably hydroxypropyl (meth)acrylate (only up to 10 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 10 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 8 C atoms in the alcohol radical or mixtures thereof, and most preferably, hydroxypropyl (meth)acrylate (only up to 5 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 9 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 6 C atoms in the alcohol radical or mixtures thereof, are used.
Component g) is used in amounts of 0 to 40 part by weight, preferably 0 to 25, more preferably 0 to 20, and most preferably 0 to 10 parts by weight.
The polyacrylate resins A) preferably include:
a) 0.2 to 8 parts by wt. of one or more optionally functional polybutadienes with a number-average molecular weight of 500 to 5,000 and a structure which is at least 30% 1,2-vinyl,
b) 10 to 40 parts by wt. styrene,
c) 15 to 45 parts by wt. hydroxyethyl acrylate, hydroxyethyl methacrylate, butane-1,4-diol monoacrylate or mixtures thereof,
d) 10 to 50 parts by wt. of at least one cycloaliphatic ester of acrylic and/or methacrylic acid having 1 to 12 C atoms in the alcohol component,
e) 10 to 40 parts by wt. of at least one aliphatic ester of acrylic and/or methacrylic acid having 1 to 8 C atoms in the alcohol component,
f) 0.3 to 4 parts by wt. acrylic acid, methacrylic acid, or a maleic or fumaric acid half-ester having 1 to 8 C atoms in the alcohol component or mixtures thereof and
g) 0 to 25 parts by wt. acrylonitrile, methacrylonitrile, hydroxypropyl (meth)-acrylate (only up to 10 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 10 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 8 C atoms in the alcohol radical or mixtures thereof,
the sum of the parts by wt. of components a) to g) being 100.
The polyacrylate resins A) more preferably include:
a) 0.3 to 7.5 parts by wt. of one or more optionally functional polybutadienes with a molecular weight of 500 to 3,000 and a structure which is at least 40% 1,2-vinyl,
b) 15 to 35 parts by wt. styrene,
c) 20 to 40 parts by wt. hydroxyethyl acrylate, hydroxyethyl methacrylate or mixtures thereof
d) 15 to 45 parts by wt. sobornyl acrylate, Isobornyl methacrylate, cyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexyl (meth)acrylate, 4-tert-butylcyclo-hexyl (meth)acrylate or mixtures thereof,
e) 10 to 40 parts by wt. of at least one aliphatic ester of acrylic and/or methacrylic acid having 1 to 8 C atoms in the alcohol component,
f) 0.5 to 3 parts by wt. acrylic acid, methacrylic acid or mixtures thereof and
g) 0 to 20 parts by wt. hydroxypropyl (meth)acrylate (only up to 10 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 10 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 8 C atoms in the alcohol radical or mixtures thereof,
the sum of the parts by wt. of components a) to g) being 100.
The polyacrylate resins A) most preferably include:
a) 0.4 to 6 parts by wt. of one or more optionally functional polybutadienes with a molecular weight of 500 to 2,000 and a structure which is at least 45% 1,2-vinyl,
b) 15 to 25 parts by wt. styrene,
c) 25 to 35 parts by wt. hydroxyethyl acrylate, hydroxyethyl methacrylate or mixtures thereof,
d) 20 to 30 parts by wt. sobornyl acrylate,
e) 15 to 25 parts by wt. of at least one aliphatic ester of acrylic and/or methacrylic acid having 1 to 4 C atoms in the alcohol component,
f) 0.5 to 2 parts by wt. acrylic acid, methacrylic acid or mixtures thereof, and
g) 0 to 10 parts by wt. hydroxypropyl (meth)acrylate (up to 5 parts by wt.), vinyl esters of aliphatic optionally branched monocarboxylic acids having 1 to 9 C atoms in the acid radical, di(cyclo)alkyl esters of maleic and/or fumaric acid having 1 to 6 C atoms in the alcohol radical or mixtures thereof,
the sum of the parts by wt. of components a) to g) being 100.
Suitable starting materials a) for the graft copolymers A) are the polybutadienes which have at least 20% of lateral 1,2-vinyl double bonds.
Polybutadienes with a content of vinylic double bonds of xe2x89xa730% are preferably suitable. The remainder of double bonds in this case can comprise any desired ratio of 1,4-cis and 1,4-trans structure. Polybutadienes which additionally also have double bonds in cyclic structures are also suitable as component a). An especially preferred starting material is a product with xe2x89xa745% of 1,2-vinyl double bonds.
Isomer mixtures of polybutadienes will in general be employed, e.g. polybutadienes which contain 30 to 90% of 1,2-vinylic double bonds, 10 to 70% of mixtures of 1,4-cis and 1,4-trans double bonds and 0 to 30% of cyclic contents. The polybutadienes can furthermore optionally carry functional groups, e.g. hydroxyl groups, carboxyl groups etc.
Such polybutadienes of different configuration are known, e.g. xe2x80x9cMakromolekule [Macromolecules]xe2x80x9d by H. G. Elias, 4th edition, Hxc3xcthig und Wepf-Verlag, Basle, Heidelberg, New York, pages 676 and 744 to 746 and 1012 et seq.
The monomers and oligomers a) to g) are in general incorporated into the graft copolymer in the same ratios as they are employed for the polymerization. The units incorporated are substantially randomly distributed.
Suitable solvents in the preparation of component A) include aliphatic, cycloaliphatic and/or aromatic hydrocarbons, such as alkylbenzenes, e.g. toluene and xylene; esters, such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, acetates with longer alcohol radicals, butyl propionate, pentyl propionate, ethylene glycol monoethyl ether acetate and the corresponding methyl ether acetate; ethers, such as ethylene glycol acetate monomethyl, -ethyl or -butyl ether; ketones, such as methyl ethyl ketone, methyl isobutyl ketone and methyl n-amyl ketone, and lactones; and mixtures of such solvents.
Graft copolymers A) can be prepared continuously or discontinuously. In the continuous preparation, the monomer mixture and the initiator are metered uniformly and continuously into a polymerization reactor and the corresponding amount of polymer is removed continuously at the same time. Copolymers which chemically are virtually uniform can preferably be prepared in this way or can also be synthesized by a discontinuous preparation in which the monomer mixture and the initiator are metered into the polymerization reactor at a constant rate without removing the polymer.
The grafting copolymerization is generally carried out in the temperature range from 140 to 240xc2x0 C., preferably 160 to 210xc2x0 C., and more preferably 165 to 200xc2x0 C., under a pressure of up to 25 bar. The initiators are employed in amounts of 0.05 to 15 wt. %, preferably 1 to 10 wt. %, and more preferred 2 to 8 wt. %, based on the total amount of components a) to g).
Suitable initiators for the preparation of graft copolymers A) are known azo- or peroxide-based free-radical initiators, but only those which have a half-life of approx. 5 seconds to approx. 30 minutes sufficiently long for the polymerization in the above mentioned temperature range. Examples of suitable initiators include 2,2xe2x80x2-azobis-(2-methylpropane-nitrile), 2,2xe2x80x2-azobis-(2-methylbutanenitrile), 1,1xe2x80x2-azobis(cyclohexane-carbonitrile), tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethyl-acetate, tert-butyl peroxyisobutyrate, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-tert-butylperoxycyclohexane, tert-butyl peroxy-3,5-5-trimethylhexanoate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, dicumyl peroxide, tert-butyl cumyl peroxide, di-tert-butyl peroxide and di-tert-amyl peroxide.
Graft copolymers A) are valuable binder components for two-component coating compositions. In this connection, xe2x80x9ctwo-component coating compositionsxe2x80x9d are to be understood as both xe2x80x9cone-pot systemsxe2x80x9d and xe2x80x9ctwo-pot systemsxe2x80x9d. Since the polymer resins according to the invention are binder components for two-component lacquers, the lacquers contain a hardener component in addition to the polymer resins according to the invention (and optionally further polyhydroxy compounds and/or aminic reactive thinners). If this hardener is, for example, a polyisocyanate with free isocyanate groups, the ready-to-use coating compositions can be prepared by mixing the components just shortly before their processing. In such a case this would be a xe2x80x9ctwo-pot systemxe2x80x9d.
However, if the hardener is a compound which reacts with the polymer resins according to the invention only at elevated temperature, for example polyisocyanates with blocked isocyanate groups, the hardener can also already be combined with the polymer resin at room temperature to give a xe2x80x9cone-pot systemxe2x80x9d which can be stored at room temperature.
In one use according to the invention graft copolymers A) are employed as a mixture with other organic polyhydroxy compounds known from polyurethane coating technology as the polyhydroxy component and/or as a mixture with aminic reactive thinners. These other polyhydroxy compounds can be the known polyester, polyether, polycarbonate, polyurethane or polyacrylate polyols. If such compounds are employed in addition to graft copolymers A) the polyacrylate polyols and/or polyester polyols of the prior art are preferred. In the case of the aminic reactive thinners, these can be products with blocked amino groups, such as aldimines, ketimines, or oxazolanes, or those which contain amino groups which are still free but are weakened in their reactivity, such as aspartic acid esters. As a general rule, the aminic reactive thinners contain more than one (blocked) amino group, so that they contribute towards building up the polymeric coating film network during the crosslinking reaction.
In the use according to the invention graft copolymers A) can be employed as a mixture with up to 70, preferably up to 50 wt. % of other polyols and/or aminic reactive thinners of the type mentioned by way of example. However, the graft copolymers essential to the invention are preferably employed as the sole polyol component in the use according to the invention.
The hydroxyl group content of graft copolymers A) is 1.07 to 8.51 wt. %, preferably 1.77 to 7.77 wt. %, more preferably 2.62 to 7.04 wt. %, and most preferably 3.27 to 6.31 wt. %.
Suitable reaction components B) binder compositions are crosslinking reagents which react with the hydroxyl groups of the graft copolymer resins, including blocked or non-blocked polyisocyanates; aminoplast resins, e.g. corresponding melamine derivatives, such as alkoxylated melamine resins, or melamine-formaldehyde condensation products (e.g. FR-A 943 411, from D. H. Salomon in xe2x80x9cThe Chemistry of Organic Filmformersxe2x80x9d, pages 235-240, John Wiley and Sons, Inc., New York, 1974); and other known crosslinking agents, which are reactive with alcoholic hydroxyl groups, e.g. epoxides, carboxylic acid anhydrides, phenoplast resins, resol resins, urea resins or guanidine resins and mixtures thereof.
Preferred reaction components B) binder compositions are commercially available, optionally blocked lacquer polyisocyanates, i.e. the known modification products containing urethane groups, uretdione groups, allophanate groups and, in particular, biuret groups, isocyanurate groups and iminooxadiazinedione groups, and prepared from monomeric diisocyanates, such as 1,6-diisocyanatohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane(isophorone-diisocyanate), 4,4xe2x80x2-diisocyanatodicyclohexylmethane, 1,4-diisocyanatocyclohexane, 1-methyl-2,4-diisocyanatocyclohexane and its mixtures with up to 35 wt. %, based on the total mixture, of 1-methyl-2,6-diisocyanatocyclohexane, 2,4-diisocyanatotoluene and its mixtures with up to 35 wt. %, based on the total mixture, of 2,6-diisocyanatotoluene or mixtures thereof. The corresponding xe2x80x9clacquer polyisocyanatesxe2x80x9d with aliphatically and/or cycloaliphatically bonded free isocyanate groups are especially preferred. A suitable polyisocyanate which does not contain the above mentioned groupings is 4-isocyanatomethyl-1,8-octane-diisocyanate. Suitable blocking agents for the blocked polyisocyanates optionally employed include xcex5-caprolactam, butanone oxime, triazole, phenol and phenol derivatives, secondary amines and malonic acid alkyl esters.
The lacquer polyisocyanates containing urethane groups include the reaction products of 2,4- and/or 2,6-diisocyanatotoluene or 1-methyl-2,4- and/or 1-methyl-2,6-diisocyanatocyclohexane with less than stoichiometric amounts of trimethylol-propane, or mixtures thereof with simple diols, such as the isomeric propane- or butanediols. The preparation of such coating polyisocyanates containing urethane groups in a practically monomer-free form is described, for example, in DE-A 1 090 196.
The lacquer polyisocyanates containing biuret groups include, in particular, those based on 1,6-diisocyanatohexane, the preparation of which is described, for example, in EP-A 0 003 505, DE-A 1 101 394, U.S. Pat. No. 3,358,010 or U.S. Pat. No. 3,903,127.
The preferred lacquer polyisocyanates containing isocyanurate groups include, in particular, the trimers and co-trimers of the diisocyanates mentioned above, such as the polyisocyanates containing isocyanurate groups which are based on diisocyanatotoluene according to GB-A 1 060 430, GB-A 1 506 373 or GB-A 1 485 564, the co-trimers of diisocyanatotoluene with 1,6-diisocyanatohexane, which may be prepared, for example, in accordance with DE-A 1 644 809 or DE-A 3 144 672, and, in particular, the aliphatic, the aliphatic-cycloaliphatic and the cycloaliphatic trimers or co-trimers based on 1,6-diisocyanatohexane and/or isophorone-diisocyanate, which are obtainable, for example, in accordance with U.S. Pat. Nos. 4,324,879, 4,288,586, DE-A 3 100 262, DE-A 3 100 263, DE-A 3 033 860 or DE-A 3 144 672. The lacquer polyisocyanates employed in the use according to the invention in general have an isocyanate content of 5 to 25 wt. %, an average NCO functionality of 2.0 to 5.0, preferably 2.8 to 4.0, and a residual content of monomeric diisocyanates used for their preparation of less than 2 wt. %, preferably less than 0.5 wt. %. Any desired mixtures of the lacquer polyisocyanates mentioned can of course also be employed.
In the high-solids two-component polyurethane coating compositions the polyol component and the polyisocyanate component are present in amounts corresponding to an equivalent ratio of isocyanate groups to hydroxyl groups of 5:1 to 1:2, preferably 3:1 to 1:1.5, and more preferably 1.5:1 to 1:1.2. The two-component coating compositions obtained by mixing the two components have only a limited processing time of approx. 1 to 24 hours and are processed either as such (solvent-free clear lacquers), or preferably using the known additives. These additives can be added either to the mixture or to the individual components before mixing thereof.
Suitable additives include solvents, such as ethyl acetate, n-propyl acetate, iso-propyl acetate, n-butyl acetate, n-hexyl acetate, n-heptyl acetate, 2-ethylhexyl acetate, methoxypropyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, mixtures of higher aromatics, white spirit or any desired mixtures of these solvents.
Further additives include plasticizers, such as tricresyl phosphate, phthalic acid diesters and chloroparaffins; pigments and fillers, such as titanium dioxide, barium sulfate, chalk and carbon black; catalysts, such as N,N-dimethylbenzylamine, N-methylmorpholine, zinc octoate, tin(II) octoate or dibutyltin dilaurate; flow agents; thickeners; stabilizers, such as substituted phenols; organofunctional silanes as adhesion promoters; light stabilizers; and UV absorbers. Such light stabilizers include sterically hindered amines, such as are described in DE-A 2 417 353 (U.S. Pat. Nos. 4,123,418 and 4,110,304) and DE-A 2 456 864 (U.S. Pat. Nos. 3,993,655 and 4,221,701). More preferred compounds include: bis-(1,2,2,6,6-pentamethylpiperid-4-yl) sebacate, bis-(2,2,6,6-tetramethylpiperid-4-yl) sebacate and n-butyl-(3,5-di-tert-butyl-4-hydroxybenzyl)-malonic acid bis-(1,2,2,6,6-pentamethylpiperid-4-yl) ester.
The moisture adhering to the fillers and pigments can be removed by drying beforehand or by using water-absorbing substances, such as e.g. molecular sieve zeolites.
Drying of the films can take place at room temperature if polyisocyanates which are free from blocking agents are used as the crosslinking agent, and requires no essential increase in temperature in order to achieve the above mentioned optimum properties. If the binders are used as a repair lacquer, however, an increase in temperature to approx. 60 to 100xc2x0 C., preferably 60 to 80xc2x0 C., for a period of 20 to 60 minutes is often advisable in order to shorten the drying and curing time. If blocked polyisocyanates or the other above mentioned product groups are used as the crosslinking agent, higher temperatures of, for example, 100 to 240xc2x0 C., preferably 110 to 220xc2x0 C. and more preferably 120 to 180xc2x0 C., must be used for the drying and curing of the films.
The coating compositions according to the invention are distinguished by a high solids and a low solvent content. The coating films resulting after curing have a high hardness, a good elasticity, an excellent resistance to weathering and chemicals and a high gloss. The curing times both for physical superficial drying and for chemical crosslinking are short, so that coated articles for use very rapidly are resistant to weathering, solvents and chemicals and can be used.
The coating compositions employed according to the invention are therefore suitable above all for coating large vehicles, such as aircraft, railway and tram carriages, lorry superstructures and the like. Another preferred field of use is their use as a car repair coating. The coating compositions are furthermore suitable for corrosion protection applications, such as e.g. coating of bridges and power masts, for general industrial, wood and furniture coating and for the first coating of cars.
The coating compositions according to the invention are applied by conventional methods, for example by spraying, pouring, dipping, brushing, atomizing or rolling. The coating compositions according to the invention are suitable both for the production of primer coats and for the production of intermediate coats, and in particular for the production of top coats on the substrate to be coated.